Measurement of heart left ventricle (LV) wall motion is used to assess human cardiac function condition. A known procedure for determining left ventricle wall motion involves imaging a patient heart (using an X-ray, MR or CT system, for example). A contrast agent is usually injected into a heart chamber to allow visualization of blood volume in a two-dimensional (2D) multi-frame image sequence (angiogram) provided by an imaging system, with each frame corresponding to a time point in the sequence. A physician visualizes the image sequence at a computer and selects one frame with the smallest LV volume and one frame with the largest LV volume. These two frames roughly correspond to end-systolic (ES) and end-diastolic (ED) phases of the heart cycle. Alternatively, the two frames may be automatically selected by employing an ECG signal acquired during the image sequence acquisition and image data processing using graphical ventricle edge detection within images, for example. Known image analysis applications may be used to analyze the two selected frames and compute quantitative data of the LV functions, one of which is wall motion. The wall motion is calculated by measuring the displacement of the cardiac wall between the two frames. Since the movements at different locations of the LV wall are non uniform, the LV wall is further divided into segments. The displacement at each segment is compared against data collected from a normal population. Well known methods for assessing cardiac wall motion include regional wall motion, centerline wall motion and radial wall motion comparison, for example.
Wall motion indicates how effectively heart muscle contracts and indicates the health of the heart. However, a 2D LV angiogram used for wall motion analysis not only contains motion caused by heart contraction, but also other motion such as breathing, or respiratory motion and patient movement. Since respiratory motion varies significantly between people and between image sequence acquisitions, it introduces inaccuracy in the calculation of wall motion of a patient and inaccuracy in comparison with predetermined population data and comparison with previous image sequence acquisitions of the same patient. Known systems employ different methods of compensating a wall motion calculation for respiratory motion. One method involves asking a patient to hold his/her breath for the duration of an imaging scan. However, this is a problem if the duration of the scan is longer than a breath-hold duration and some patients cannot hold their breath due to illness or age. Other known methods involve detection of a position change of a reference object at different respiratory phases. The reference object is usually placed around diaphragm or abdominal area of the patient, because the motion around these areas is mostly caused by breathing. However, it is difficult to choose the right position of the reference object so that the displacement of the reference object mirrors respiratory motion induced LV wall motion displacement. Another known method involves acquiring images only at the time where respiratory motion is the least. This is achieved by gating image acquisition at a desired respiratory phase with a respiratory signal provided by a respiration monitoring device. However this potentially results in a longer image sequence acquisition time.
Another known system used to remove respiratory motion from heart wall motion in X-ray images, for example, uses a simplified assumption that respiratory motion is only vertical movement (from head to toe). The respiratory motion is calculated by using the vertical movement of the diaphragm, for example. However this assumes different parts of the body move the same amount and in the same direction in response to respiration. It is known however, that even different sections of the diaphragm move in different directions. A system according to invention principles addresses the identified deficiencies and associated problems.